The long term goals of the proposed projects are to analyze the integrative capabilities of chemical transmission in a neural circuit where the neurotransmitters and the conductances of the postsynaptic responses have been characterized. We have focused our efforts on a neural circuit in the buccal ganglia of the marine snail, Aplysia californica. Several observations made during experiments aimed at identifying the neurotransmitter used by multi-action interneurons, the S1's, in this neural circuit are the bases for the proposed investigations. Pharmacological experiments during these studies indicate that snake Alpha-toxins, which are considered specific cholinergic antagonists, also block certain noncholinergic responses. Ligand binding studies using iodinated Alpha-toxin indicate that the toxin binds to a cholinergic site, even though the toxin blocks noncholinergic responses. Physiological, pharmacological and binding studies are proposed to examine the relationship between toxin binding and toxin effects and to test a hypothesis which links the binding and physiological results obtained thus far: Cholinergic and noncholinergic receptors may share the same ionophore. These studies may make a significant contribution to our understanding of mechanisms of drug actions in the CNS as well as provide us with insights into the functional organization of receptor-ionophore complexes in neuronal membranes. In preliminary studies of frequency dependent modulation in the buccal circuit we observed that the components comprising a multicomponent response mediated by the S1 neurons in several follower cells could vary independently of each other. However, one of the components of the response co-varied together among several followers. Electrophysiological and morphological experiments are proposed to test whether the independent variation of the components of a multicomponent response occurs because one component is: (a) modulated separately from the other; (b) generated by an intercalated interneuron; or (c) generated at different sites from the other. Elucidation of these observations will lead to greater understanding and appreciation of the integrative capabilities of individual neurons.